Determination of total arsenic in food (2)

4.
Operation steps

(1) Sample digestion

①Nitric acid - perchloric acid -sulfuric acid method:

a.
Grain, vermicelli, vermicelli, bean curd products, cakes, tea, etc.
and other solid foods with low water content: Weigh 5.
00g or 10.
00g crushed sample, put it in a 250-500mL nitrogen bottle, add a little water first Make it wet, add a few glass beads and 10-15 mL of nitric acid-perchloric acid mixture, let it stand for a while, slowly heat it on a small fire, wait until the effect is relieved, and let it cool
.

b.
Vegetables and fruits: Weigh 25.
00g or 50.
00g cleaned and homogenized samples, place them in a 250～500mL nitrogen bottle, add a few glass beads, 10～15mL nitric acid-perchloric acid mixture, Follow the steps ①a to operate according to the law from "Leaving for a while.
.
.
", but every 10mL of the solution after constant volume is equivalent to 5g of sample, which is equivalent to adding 1mL of sulfuric acid
.

c.
Sauce, soy sauce, vinegar, cold drinks, tofu, fermented bean curd, pickles, etc.
: Weigh 10.
00g or 20.
00g sample (or draw 10mL or 20mL liquid sample), place it in a 250-500mL ammonia bottle, add Several glass beads, 5～15mL nitric acid-perchloric acid mixed solution
.

d.
Alcoholic beverages or carbon dioxide- containing beverages: draw 10.
00mL or 20.
00mL sample, put it in a 250～500mL nitrogen bottle, add a few glass beads, first heat it with a small fire to remove ethanol or carbon dioxide , and then add 5～ 10ml.
Nitric acid-perchloric acid mixed solution, after mixing, follow step ①a from "putting for a while.
.
.
" to operate according to the law, but every 10mL of the solution after constant volume is equivalent to 2mL sample
.

e.
Foods with high sugar content: Weigh 5.
00g or 10.
0g sample, place it in a 250～500mL nitrogen bottle, add a little water to make it wet, add a few glass beads, 5～10mL nitric acid-perchloric acid After mixing, shake well
.

f.
Aquatic products: Take the edible part of the sample and mash it into a homogenate, weigh 5.
00g or 10.
0g (seafood algae, shellfish can be appropriately reduced sampling), put it in a 250-500mL nitrogen flask, add a few glasses of glass Beads, 5-10mL nitric acid-perchloric acid mixture, after mixing, follow the steps ①a from "adding 5mL or 10mL sulfuric acid along the bottle wall.
.
.
" according to the law
.

②Nitric acid-sulfuric acid method: use nitric acid instead of nitric acid-perchloric acid mixture for operation
.

③Ashing method:

a.
Grain, tea and other foods with low water content: Weigh 5.
00g ground sample, place it in a crucible, add 1g magnesium oxide and 10mL magnesium nitrate solution, mix well, and soak for 4h
.

Do the reagent blank test according to the same operation method
.

b.
Vegetable oil: Weigh 5.
00g sample, place it in a 50mL porcelain crucible, add 10g magnesium nitrate, and then cover 2g magnesium oxide on it, heat the crucible on a low fire, and immediately remove the crucible until it smokes.
To prevent the contents from overflowing, after the smoke is small, reheat until the ashing is complete
.

c.
Aquatic products: Take the edible part of the sample and mash it into a homogenate, weigh 5.
00g, place it in a crucible, add 1g of magnesium oxide and 10mL of magnesium nitrate solution, mix well, and soak for 4h
.

(2) Determine the solution (equivalent to 2g food, 4g vegetables and fruits, 4mL cold drinks, 5g vegetable oil, other samples refer to this amount) and the same amount of reagent blank solution after digestion with a certain amount of sample.
Add 5mL potassium iodide solution (150g/L), 5 drops of acidic stannous chloride solution and 5mL hydrochloric acid to the arsenic bottle (if the sample is nitric acid-perchloric acid-sulfuric acid or nitric acid-sulfuric acid digestion solution, the sample should be subtracted The volume of medium sulfuric acid; if the digestion solution is digested by the ashing method, the volume of hydrochloric acid in the sample should be subtracted), and then add an appropriate amount of water to 35mL (no more water for vegetable oil)
.

5.

Where x-the content of arsenic in the sample, mg/kg or mg/L

m ₁ ——The quality of arsenic in the digestion solution of the sample for determination, ug

m ₂ ——The quality of arsenic in reagent blank, ug

m——mass or volume of sample, g or mL

V ₁ ——Total volume of sample digestion solution, mL

V ₂ ——The volume of the digestion solution of the test sample, mL

The calculation result retains two significant digits

The absolute difference between two independent determination results obtained under repeatability conditions shall not exceed 20% of the arithmetic mean
.